The present invention refers to an actuation device, and to a system for blocking, in a predetermined position, the drum of a machine for washing and/or drying laundry, using such an actuation device.
Actuation devices of the above type are generally known and used in several fields; they usually consist of an actuator having at least an actuation element, movable between at least a respective first position and a respective second position, and vice-versa, and a transmission element capable of moving from a respective first operating condition to a respective second operating condition, under the action of said actuation element.
Among the actuation devices of the cited type, those using a thermal actuator have, for instance, a significant importance, by virtue of their simple and economical manufacture, and their high reliability. Their further advantages are constituted the notable power they can develop, in view of their contained dimensions, and, above all, their operating noiselessly.
Thermal actuators, also known as thermo-actuators, usually have a housing made of a thermal conductive material (for example metal), which is connected to an electric heater. Within the housing, there are contained a thermally expansible material (such as a wax) and a piston which constitutes the actuation element; the electric heater is usually a positive temperature coefficient resistor, or PTC, which is electrically supplied through two terminals.
When a voltage is applied to the supply terminals, current passes through the electric heater, so that the latter generates heat and causes expansion of the thermally expansible material. The expansion, in turn, causes linear displacement of the piston, towards the outside of the housing, until a predetermined position, usually set through a mechanical end-of-stroke, is attained, which can be defined as a final working position.
Upon interruption of the electric supply, the heater and housing of the thermo-actuator cool down, and the thermally expansible material shrinks, thereby causing the piston to return to the initial rest position, with the aid of a return elastic element, such as a spring.
One of the peculiar features of thermal actuators, or thermo-actuators is their working slowness, which is determined by the necessary times for heating and cooling the thermally expansible material, with the relevant expansion or shrinking, and resulting piston movement.
As said above, this fact does not limit the use of thermal actuators in a wide range of fields, where the operating speed of the device is not crucial, either during the electric supply phase or during the return phase to the initial rest position.
Similar considerations can also be made in connection with other type of actuators, which are characterized by a certain slowness in movement during return to the initial rest position, such as for instance those based on the use of electric motors and/or gear-reducers, which operate rotating cams having a shaped profile.
For some applications, however, it is convenient to have an actuation device based on the use of a thermo-actuator which, during at least one of its operating phases, is able to produce movement faster than that imposed by the simple heating or cooling speed, and resulting expansion or shrinking, of the thermally expansible material. Similarly, in the case of an actuation device based on an electric motor and/or a gear-reducer, which rotates a shaped profile cam, it could be convenient to have movement of the cam towards a respective operating condition which is faster than that imposed by the simple speed of angular movement of the motor which operates the cam.
The present invention is based on the acknowledgment of the above facts and, within such a framework, has the purpose of providing an actuation device which, at least during a respective operating phase, can produce movements that are faster than those imposed by the actuation times and/or the intrinsic speed of the relevant actuation means, the faster movements being, in particular, obtained in a terminal period of the operating phase of the actuation means.
A further aim of the invention is that of providing an actuation device which is capable of realizing at least a type of actuation which is delayed with respect to the instant when the actuator of the actuation device starts to move towards one of its possible end-of-stroke conditions.
A further aim of the invention is that of providing a system for blocking, in a predetermined position, the drum of a machine for washing and/or drying laundry, using such an actuation device.
The foregoing aims are attained, according to the present invention, by an actuation device and a system for blocking, in a predetermined position, the drum of a machine for washing and/or drying laundry, having the features of the annexed claims, which form an integral part of the present description.
Further aims, features and advantages of the present invention will be apparent from the following detailed description and the annexed drawings, which are supplied purely as a non limiting example.